1. Field of the Invention
The present invention relates to a specimen stage, and particularly relates to a stage-positioning mechanism used in a charged particle beam apparatus such as an electron microscope for measurement, inspection or observation in the field of semiconductor device fabrication.
2. Background Art
A large number of specimen stages in electron microscope units for semiconductor inspection include a stop mechanism to obtain a static image after the positioning is completed. One form of such a stop mechanism in a stage utilizes friction as in the case of a constant friction brake. Another stop mechanism utilizes an ultrasonic motor which serves as both the stop mechanism and a driving mechanism
The constant friction brake and the ultrasonic motor needs a surface member to generate a friction force, and these stop mechanisms generate heat. Particularly in a vacuum environment where the thermal conductivity is low, the friction heat causes a temperature gradient in the surface member. The temperature gradient causes the heat to flow in the surface member. A position where the temperature is high in the surface member is taken as a reference position (hereinafter referred to as a thermal-deformation reference position) where thermal expansion and thermal contraction after the thermal expansion occur. At the time of observation with the electron microscope, these thermal expansion and thermal contraction cause the stage to move, and thereby an image of a measured object is observed to be drifting. Particularly, the larger the distance is between the stop position of the stage and the heat generation reference position, the larger the amounts of thermal expansion and thermal contraction of the surface member are.
As a technique to avoid the stage movement due to these thermal expansion and thermal contraction, Patent Document 1 discloses a so-called servo control technique in which the position of a stage is monitored in real time and then a feedback is performed on a deflection amount of electron beam and a motor while following the behavior of a table.
Moreover, Patent Document 2 proposes an approach in which the temperature of a whole stage is controlled and thus maintained at a certain point, thereby reducing a thermal expansion amount and a thermal contraction amount. Furthermore, Patent Document 3 discloses a technique which attempts to minimize a heat generation amount by adopting an active brake to reduce a friction heat.
Patent Document 1: Japanese Patent Application Publication No. 2007-042514
Patent Document 2: Japanese Patent Application Publication No. 2007-019279
Patent Document 3: Japanese Patent Application Publication No. 2006-237069